Electronic Structure of Interfaces between Thiophene and TiO₂ Nanostructures

Abstract

We investigated the electronic properties of hybrid combinations of organic−inorganic interfaces relevant for photovoltaic applications, a thiophene (molecule or polymer) and a TiO 2 -anatase nanostructure, using ab initio density functional theory (DFT) and many-body perturbation theory calculations for model systems. The DFT results concerning electronic charge distribution show interface states coupling the polymer to the oxide substrate at the molecule's lowest unoccupied state, favoring electron transfer from the organic to the oxide through photoexcitation. Concerning the energy level structure, DFT predicts a virtually zero effective energy gap between polymer valence and oxide conduction bands. The GW-based results lead to proper band alignment, restoring the interface energy gap, and at the same time highlight the confinement effects to be expected for oxide nanostructures.

The GW Compendium: A Practical Guide to Theoretical Photoemission Spectroscopy

“…Also, computed optical and RAS spectra agree well with experimental spectra for these systems. Later calculations for more complex surfaces or surface adsorbates have to be taken with a grain of salt, since they may not be fully converged with respect to all computational parameters, unless plasmon pole models, other model dielectric functions, or cluster models were used (Giorgi et al, 2011; Patrick and Giustino, 2012; Alves-Santos et al, 2014).…”

Electronic and optical properties of doped TiO2 by many-body perturbation theory

“…For instance, hybrid functionals often overestimate the TiO 2 band gap thus leading to an uncertainty in the position of the impurity levels. 12 Recent many-body perturbation theory (MBPT) studies [13][14][15][16] of the band structure and absorption spectrum of pristine TiO 2 have in fact provided evidence that approaches beyond DFT are required for a quantitative description of photoemission and light absorption experiments in this material.…”

Global and local aspects of the surface potential landscape for energy level alignment at organic-ZnO interfaces

“…The adverse scaling of GW with the number of atoms in the system and the slow convergence of quasiparticle energies with respect to the number of unoccupied states that are included in the calculation pose serve challenges to the tractable system size, which is easily exceeded by most surface adsorbate systems of interest. Nonetheless, an increasing number of GW calculations for organic adsorbates on surfaces is being reported in the literature [96,97,98,99,100,101,102,103,104,105,106,107,108,109].…”